Space Station training instructor Bill Todd is the project manager for NEEMO, and he commanded the first mission - a one-week stay inside Aquarius. He was joined by two NASA astronauts - Mike Gernhardt and Mike Lopez-Alegria - and Canadian Space Agency astronaut Dave Williams.

On the first day of the mission, Williams wrote in his journal: "In contrast to the eight and a half minute flight to space where 7 million pounds of thrust were propelling us to low earth orbit, the leisurely swim to the habitat seemed quite surreal ... We left the habitat at 10:04 - four aquanauts embarking on their first real dive from an underwater habitat."

In May 2002, the second NEEMO crew took the plunge. Space Station trainer Marc Reagan accompanied NASA astronauts Sunita Williams, Dan Tani and Mike Fincke for a one-week stay in Aquarius.

Reagan commented in his Mission Day 2 journal entry: "At noon today ... we officially became aquanauts. Not 'certified trained as aquanauts,' not 'wannabe aquanauts,' but real aquanauts. Welcome to a pretty exclusive club. In case you were wondering, there is no door prize, but the job benefits are outstanding. Technically, the term aquanaut is limited to those who stay underwater for 24 hours or more."

The third NEEMO mission followed two months later, this time with Jonathan Dory, a human factors expert from Johnson Space Center's Habitability and Environmental Factors Office. Dory was joined by three astronauts - Greg Chamitoff, Danny Olivas and Jeff Williams.

One of the experiments conducted during NEEMO 3 was the construction of an underwater structure. The experiment would provide an analog of space station assembly during extravehicular activities, or EVAs.

After successfully completing the task, Dory wrote in his journal: "Working with complex assemblies while using tools, managing time, air, and buoyancy, all came together to provide an excellent analogy for performing EVA assembly operations on the International Space Station. Knowing that successfully completing waterlab would be difficult, we all worked together to formulate a plan for assembling waterlab before we came down to Aquarius. We took the large assembly, and thought of it in terms of separate smaller assemblies, then created a new set of schematics to illustrate each small assembly and how they all fit together - a classic case of divide and conquer. In the end, we were able [to] put together the whole assembly in half the time we initially planned."

Two tropical weather systems threatened the NEEMO 4 expedition in September 2002. The NEEMO 4 crew included Flight Director Paul Hill, two astronauts - Scott Kelly and Rex Walheim - and Jessica Meir, a support scientist for the International Space Station. The mission was delayed due to Hurricane Isadore, forcing NURC managers to shorten it to an underwater duration of five days. Then, three days into their underwater mission, the crewmembers were told that Tropical Storm Lili was headed in their direction and to prepare for an early departure from Aquarius. Fortunately, Lili degenerated to the point where it was no longer a threat, so the crew was able to remain the full five days.

Upon returning to the surface, Meir wrote in her journal: "I hope that the NOAA/NASA relationship continues to grow, as I believe a significant potential for benefit on both sides exists through Aquarius."

As of August 2004, NEEMO 5 was the longest expedition to date. The crew, commanded by astronaut Peggy Whitson, stayed underwater for 14 days. Joining Whitson were two other astronauts, Clayton Anderson and Garrett Reisman, and International Space Station support scientist Emma Hwang.

Whitson was the first Space Station Expedition crewmember to live aboard Aquarius, so she was able to offer a unique perspective. She wrote in her journal: "I have spent a lot of time in the last [six] months wishing that I were back living on the International Space Station ... This longing to be in space is probably why this opportunity to have a mission under the sea intrigued me."